How to import Downloaded Materials/Files?
Blender has no specific file formats for objects, materials, shaders and so on. To reuse the material from one .blend file in another, you can either create a link to the material in your material blend or you can append said material. 

Linking materials is a great way to create material libraries. If you make changes to the material blend, those changes will be visible in all files that have links to the material file, as soon as you open or reload them.

Appending materials creates copies of the source material in your current blend file. 

The process for both methods is the same. 


Open the file you want to link/append the material to.
Go to "Files - Link/Append"
Navigate to the .blend that contains the material and click on it
Open the Material Folder and double-click on the material you want to link/append.




After that, your material should be visible in the Material selector.